Previous studies in miniature swine have demonstrated that products of the class II region of the major histocompatibility complex (MHC) are of overwhelming importance in determining the fate of vascularized allografts, and it is likely that the same is true in human beings. In addition, it has recently been demonstrated in a mouse model that reconstitution of myeloablated animals with syngeneic bone marrow cells, transduced with an allogeneic MHC gene leads to specific prolongation of survival of skin grafts bearing the same alloantigen. In preliminary studies, the transfer of class II genes by bone marrow transplantation from an intra-MHC recombinant donor, led to long-term tolerance to a subsequent renal allograft class II matched to the bone marrow donor but completely mismatched to the recipient. Taken together, these results suggest that transfer of genes encoding class II antigens could provide a new approach to the induction of specific transplantation tolerance across complete histocompatibility barriers. The overall goal of this project is to introduce allogeneic class II genes into autologous bone marrow cells of miniature swine via retroviral transduction and to determine the effects of this procedure on parameters of transplantation immunity. cDNA clones corresponding to all expressed class II genes from two SLA haplotypes have previously been isolated and sequenced in this laboratory. The specific aims of this proposal are to: 1) Construct recombinant retroviruses containing SLA class II cDNAs under the transcriptional control of constitutive promoters; 2) Establish conditions for introduction of allogeneic class II genes into bone marrow stem cells via these recombinant retroviral vectors; 3) Reconstitute myeloablated miniature swine with autologous bone marrow cells transduced with allogeneic class II cDNAs, and examine the expression of the introduced genes; and 4) Determine the effects of class II gene transfer on the induction of transplantation tolerance as detected by in vitro and in vivo assays. These studies could have important implications for the use of gene transfer technology in the manipulation of immune responses to both allogeneic and xenogeneic transplants in the future.